lkml.org 
[lkml]   [2008]   [Jan]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
FromBodo Eggert <>
SubjectRe: [patch 2/2] 8250_pnp: register x86 COM ports at the conventional ttyS names
DateWed, 16 Jan 2008 21:33:04 +0100
Bjorn Helgaas <bjorn.helgaas@hp.com> wrote:
> On Wednesday 16 January 2008 11:44:37 am H. Peter Anvin wrote:
>> Bjorn Helgaas wrote:

>> > +#ifdef CONFIG_X86
>> > + switch (port->iobase) {
>> > + case 0x3f8: return 0; /* COM1 -> ttyS0 */
>> > + case 0x2f8: return 1; /* COM2 -> ttyS1 */
>> > + case 0x3e8: return 2; /* COM3 -> ttyS2 */
>> > + case 0x2e8: return 3; /* COM4 -> ttyS3 */
>> > + }
>> > +#endif
>> > +
>>
>> Arguably, the right thing is to use the addresses present in the array
>> at address 0x400. In particular, COM3 and COM4 aren't always at those
>> addresses.
>
> Wow. I bow before your storehouse of x86 arcana :-)
>
> I guess you're referring to the "BIOS data area," which I'd never
> heard of before (but fortunately, Google knows).

You'll want to google for Ralph Brown ...
if your back allowes bowing that much.

> What would you think about doing this only for COM1 and COM2? The
> only real value for doing this in the first place is so "console=ttyS0"
> always goes to COM1, even if we don't have SERIAL_PORT_DFNS. User-
> space ought to use some sort of udev magic if it cares about persistent
> naming.

Since the first four COM ports are magic, and since using the BIOS port
numbers will move the non-legacy ports anyway, you should use all up to
four stored port numbers.

BTW1: These addresses may be used to detect ports on non-standard addresses,
but unfortunately they don't tell the IRQ.

BTW2: When I submitted a patch using the BIOS data area, I was told that it
might not exist on systems booting from non-PC firmware. This claim was not
yet backed with any knowledge, nor did anybody suggest a way to detect this
situation.



\
 
 \ /
  Last update: 2008-01-16 21:37    [from the cache]
©2003-2010